And how is the multitouch performed ? Is this the responsibility of the multitouch sample programs that Johny is using ? To respond to all IR sources that are available out there ?

I haven't used Johnny's multitouch sample programs.But once you've done the calibration, you can use all available IR sources (up to 4), like you said.The "hard work" in multitouch software is to use those "cursor positions" to achieve the desired behavior (like scaling or rotating of an image).